Islamic State jihadists have released a video condemning presidential elections in Tunisia(YouTube)

Islamic State (Isis) militants have claimed responsibility for the murders of two Tunisian politicians and urged Muslims in the northern African country to join the extremist group in a video posted online.

Three bearded Tunisians fighters wearing black fatigues are seen in the footage saying they killed left wing politicians Mohammed Brahmi and Chokri Belaid in 2013.

"Yes, tyrants, we're the ones who killed Chokri Belaid and Mohamed Brahmi," one of the jihadists identified by Tunisian authorities as Abou Mouqatel, also known as Boubakr Hakim, says in the video, according to AFP.

"We are going to come back and kill several of you. You will not have a quiet life until Tunisia implements Islamic law."

Hakim, a 31-year-old French native, was the main suspect for the double murder. Tunisia's Interior Ministry has confirmed he is the militant appearing in the video.

The government initially blamed Tunisian extremist group Ansar al-Sharia for the murders. It has links to al-Qaeda.

In the video, the Islamism militants also condemn Tunisia's presidential elections that are to be held this weekend.

The country has recently marked the fourth anniversary of the self-immolation of Mohammed Bouazizi, a fruit seller who killed himself in a protest against police triggering the first Arab Spring revolution.